Method and system for vaporizing and superheating cryogenic fluids

ABSTRACT

1,175,308. Valves. BLACK, SIVALLS &amp; BRYSON Inc. 5 March, 1968 [14 March, 1967], No. 10722/68. Heading F2V. [Also in Divisions F4 and G3] A valve adapted to transmit only the higher of two pressure signals 21, 23 transmitted thereto comprises a pair of diaphragms 29, 31 which are biased downwards by signal 21 and upwards by signal 23 such that when signal 21 is the higher, as shown, diaphragm 31 is unseated to admit signal 21 to outlet 24. Diaphragm 29 is unseated when signal 23 is the higher.

7. 1968 c. E. SMALLING 3,398,723

METHOD AND SYSTEM FOR VAPORIZING AND SUPERHEATING GRYOGENIC FLUIDS Filed March 14, 1967 2 Sheets-Sheet l VAPOR OUT J r5 ls 2 HEATER/ J3 LIQUIDIN -l SUPPLY F L0 w TEMPERATURE CONTROL 'CONTROLLER F 7 s 43 42 J j SUPPLY BIASING 21 23 '"RE LAY f 22 IO M SELECT RELAY j j J 39 24 I4 40 AIR IN FUEL m f INVENTOR.

CHARLES E. SMALLING ATTORNEY 3,398,723 METHOD AND SYSTEM FOR VAPORIZING AND SUIIJHHEATING Aug. 27, 1968 c. E. SMALLING CRYOGENIC FLUIDS 2 Sheets-Sheet 2 Filed March 14, 1967 FIG. 3

FIG. 4

INVENTOR.

CHARLES E. SMALLING BY MW ATTORN EY United States Patent O 3,398,723 METHOD AND SYSTEM FOR VAPORIZING AND SUPERHEATING CRYOGENIC FLUIDS Charles E. Smalling, Oklahoma City, Okla., assignor to Black Sivalls & Bryson, Inc., Kansas City, Mo., a corporation of Delaware Filed Mar. 14, 1967, Ser. No. 623,054 7 Claims. (Cl. 122356) ABSTRACT OF THE DISCLOSURE The present invention relates to an improved method and system for vaporizing and superheating cryogenic fluids, and more particularly, to an improved method and system for convectively heating cryogenic fluids wherein the fluids are vaporized and superheated to a desired temperature under constant or varying throughput conditions.

Background of the invention The present invention relates to an improved method and system for vaporizing and superheating cryogenic fluids. Cryogenic fluids are those fluids which can exist in the liquid phase only at very low temperatures when at moderate pressures. Such fluids are commonly stored in the liquid phase, and are subsequently converted to the vapor phase for use. For example, liquified natural gas is commonly utilized in the natural gas industry for meeting peak natural gas demands. In areas where natural gas is not locally produced it must be transported by pipeline from remote producing fields. During periods of peak gas consumption, such as a prolonged cold spell, the demand for natural gas may exceed the capacity of the pipeline. When this condition exists, the stored liquified natural gas is vaporized, superheated to prevent subsequent condensation, and injected into the pipeline in order to meet the demand.

Prior to the present invention many attempts have been made with little success to vaporize and superheat cryogenic fluids by directly heating the fluids. These prior attempts have utilized fluid heaters in which the fluid to be heated is conveyed through tubes in a furnace and heat is transferred to the fluid by radiation and convection from combustion gases and flames in the furnace. Due to the very low temperature of cryogenic fluids (approximately 260 F. for liquified natural gas) water vapor condenses on the tubes in the furnace causing layers of ice to form on the outside of the tubes. These layers of ice then reflect radiant heat from the combustion flames in the furnace preventing proper vaporization and superheating of the cryogenic fluids conveyed through the tubes. Prior attempts have failed to overcome this problem. In addition, prior attempts to use direct fired heating of cryogenic fluids have failed due to the utilization of inadequate control systems.

Because of the failure of methods including direct radiant heating hereinbefore described, methods for vaporizing and superheating cryogenic fluids indirectly have been proposed. These methods include directly heating a fluid such as isopentane or water in a furnace, conducting the hot isopentane or water to a heat exchanger, and exchanging heat with the fluid to be vaporized and superheated. These indirect heating methods require expensive and elaborate apparatus, and in addition, fail to achieve adequate heating control. It is essential in most applications that the method for vaporizing and superheating cryogenic fluids achieve close heating control. That is, when the flow rate of fluid to be vaporized and superheated changes, the heat transferred to the fluid must also im- 3,398,723 Patented Aug. 27, 1968 mediately change so that all the fluid in the liquid phase is vaporized and superheated the desired amount. For example, in the application where liquified natural gas is being vaporized for distribution to domestic consumers, condensation of the gas after vaporization would be detrimental. Therefore, it is essential that a level of superheat be maintained at all times. Quite often sudden increases in the flow of the liquified natural gases required are encountered. These flow increases cause a drop in the quantity of superheat imparted to the gas, and unless the heat input is immediately increased inadequate superheating or even inadequate vaporization of a portion of the liquified natural gas results. The indirect methods utilizing isopentane or water inherently include slow response to sudden changes in flow since the 'heat input to the intermediate heat transfer fluid must be first increased before the heat input to the fluid being vaporized and superheated can be increased.

The present invention provides a method and system for vaporizing and superheating cryogenic fluids whereby direct heating of the fluid is accomplished and close control of the heat content of the fluid being heated is achieved.

Summary of the invention The present invention is directed to a method and system for vaporizing and superheating cryogenic fluids wherein heat is transferred to the fluid totally through convective heat transfer with no heat being transferred by radiant heat transfer. The fluid is passed through a furnace within a plurality of tubes. Fuel and air are combusted in combustion chambers attached to the furnace, and hot products of combustion are discharged into the furnace at a high velocity. Because of the very low inlet temperature of the cryogenic fluid to be vaporized water condenses on the tubes containing the fluid from the hot products of combustion. This condensed water then freezes on the tubes forming layers of ice. However, the ice has little effect on the rate of heat transferred from the hot products of combustion to the fluid since all the heat is transferred by convection and the rate of convective heat transfer is relative to the area of surface being heated rather than the material of the surface. Thus, a heating step is provided wherein heat is transferred solely by convection, the rate of which is not affected by the presence of layers of ice on the tubes containing the fluid being heated.

The present invention further provides for closely controlling the level of superheat imparted to the fluid after it has been vaporized even though the fluid flow rate may vary. This is accomplished through the provision of con trolling the volume of hot products of combustion released into the furnace in proportion to the temperature of the superheated vapors leaving the furnace and in proportion to the flow rate of fluid to the furnace.

It is, therefore, a general object of the present invention to provide an improved method and system for vaporizing and superheating cryogenic fluids wherein convective heat is transferred directly to the fluids from hot products of combustion.

A further object of the present invention is the provision of a method and system wherein cryogenic fluids are vaporized and superheated to a desired level by controlling the rate of convective heat transferred from hot products of combustion to said fluids.

It is still a further object of the present invention to provide a method and system for vaporizing and superheating cryogenic fluids by conducting the fluid to a heater and detecting the flow rate of the fluid, heating the fluid and detecting the temperature of the fluid after it is heated, controlling the heating of the fluid in a predetermined relation to the detected flow rate and the detected temperature so that said fluid is vaporized and superheated to a desired temperature.

Other and further objects, features, and advantages will be apparent from the following description of presently preferred embodiments of the invention, given for the purpose of disclosure, and taken in conjunction with the accompanyin drawings.

Description of the drawings In the drawings forming a part of the disclosure herein, like character references designate like parts throughout the several views wherein:

FIGURE 1 illustrates in diagrammatic form a system for carrying out the method of this invention,

FIGURE 2 is a sectional view of the high select relay shown in FIGURE 1,

FIGURE 3 is a front sectional elevatiOn of a heater similar to that illustrated in FIGURE 1, and

FIGURE 4 is a side sectional elevation of a heater similar to that illustrated in FIGURE 1.

Description of the preferred embodiment Referring now to the drawings, and particularly to FIGURE 1, conduit 1 leads a supply of cryogenic fluid in liquid form to a heater generally indicated by the reference numeral 2. The fluid passes through a plurality of heating tubes 3 connected in series and disposed within heater 2. The number and arrangement of heating tubes 3 is determined by standard engineering design practices taking into account such factors as the volume of fluid to be vaporized and superheated, the composition of the fluid, etc. Hot products of combustion are discharged into heater 2 from combustion chambers 4 causing convective heat to be transferred to the fluid within heating tubes 3 as will be discussed in greater detail below. The cryogenic fluid within heating tubes 3 is vaporized and superheated a desired amount. Conduit 5 leads the superheated vapor from the system to a point of use or further distribution.

Combustion chambers 4 are each capable of producing a high velocity jet of hot products of combustion and are of the type described and shown in US. Patent No. 3,265,113. Fuel and air are intimately mixed in the combustion chambers, combusted, and hot products of combustion only are discharged from the chambers. Conduit 6 leads air from a source to conduits 7 and 8. Conduit 7 leads air to one of combustion chambers 4, and conduit 8 leads air to the other of combustion chambers 4. Valve 12 in conduit 6 regulates the flow of air traveling from its source to combustion chambers 4. Conduit 9 leads fuel from a source to conduits 10 and 11. Conduit 10 leads fuel to one of combustion chambers 4, and conduit 11 leads fuel to the other of combustion chambers 4.

Valve 13 in conduit 9 regulates the flow of fuel traveling from its source to combustion chambers 4. If it is desired to regulate the flow of air and fuel to combustion chambers 4 manually, valves 12 and 13 may be manually operable. The system shown illustrates apparatus for automatically controlling the flow of fuel and air to combustion chambers 4 which is the preferred embodiment of the present invention. Valves 12 and 13 are shown as a pneumatically operable assembly generally designated by reference numeral 14.

A pair of orifice flanges and an orifice, generally designated by reference numeral 15, are installed in conduit 1. A pneumatic flow controller 16 senses the differential pressure drop of the fluid across orifice assembly 15 through conduits 17. Flow controller 16 is of the pneumatic type wherein air or other gas is supplied to the instrument at a pressure level of p.s.i.g. the instrument responds to the differential pressure across orifice assembly 15 with a proportional output pneumatic signal of from 0 to 15 p.s.i.g. No further detailed description of the orifice assembly 15 or the flow controller 16 is given since any conventional pneumatic differential pressure type of flow controller assembly may be used.

A temperature sensing element 18 is installed in conduit 5 and is connected to temperature controller 19 by conduit 20. Temperature controller 19 is also of the pneumatic type wherein air or other gas is supplied to it at a pressure level of 20 p.s.i.g., and it responds to the temperature sensed by element 18 with a proportional output pneumatic signal of from 0 to 15 p.s.i.g. No further detailed description of element 18, conduit 20, or temperature controller 19 is given since any conventional pneumatic temperature controller assembly may be used.

A first portion of the output signal from flow controller 16 is led by conduit 43 to biasing relay 44. Biasing relay 44 is a relay of the type wherein an output signal adjustably proportional to the input signal is generated. Air or other gas at a pressure level of 30 p.s.i.g. is supplied biasing relay 44 so that an output signal of from 0 to 25 p.s.i.g. may be generated in proportion to the signal generated by flow controller 16. No further description is given as any biasing relay of the type described may be used.

The output signal from biasing relay 44 is led by conduit 42 to temperature controller 19 and is used as the supply for temperature controller 19.

A second portion of the output signal from flow controller 16 is led by conduit 21 to one input connection of high select relay 22, and the output signal from temperature controller 19 is led by conduit 23 to a second input connection of high select relay 22. High select relay 22 is of the type which responds to two input pneumatic signals with one output pneumatic signal of a pressure level equal to the highest of the two input signals.

FIGURE 2 illustrates one form of such a relay. Input pneumatic signals are led into the relay by conduits 21 and 23. The pneumatic signal from conduit 21 is led by passage 25 to passages 26 and 27. Passage 26 leads a portion of the signal into chamber 28 wherein its pressure is exerted on the top surface of diaphragm 29. Passage 27 leads a portion of the signal into chamber 30 wherein its pressure is exerted on the top surface of diaphragm 31. Diaphragms 29 and 31 are flexible rubher, or other similar material, which will respond to pneumatic pressure by expanding or bulging. The input pneumatic signal from conduit 23 is led by passage 32 to passages 33 and 34. Passage 33 leads a portion of the signal into chamber 35 wherein its pressure is exerted on the bottom side of diaphragm 29, and passage 34 leads a portion of the signal into chamber 36 wherein its pressure is exerted on the bottom side of diaphragm 31. Passage 37 is located between diaphragms 29 and 31 so that its openings are adjacent to diaphragms 29 and 31. When the pressure level of the pneumatic signal on the top sides of diaphragms 29 and 31 is equal to the pressure level of the pneumatic signal exerting pressure on the bottom sides of diaphragms 29 and 31 pressure is communicated from both of chambers 30 and 35 to passage 38 through passage 37. When the pressure of the signal in chambers 28 and 30 becomes greater than the pressure of the signal in chambers 35 and 36, diaphragms 29 and 31 will bulge towards chambers 35 and 36. Diaphragm 29 will bulge against the top opening of passage 37 sealing it off. Diaphragm 31 will bulge away from the bottom opening of passage 37 allowing communication of the signal in chamber 30 with passage 38 through passage 37 as shown in FIGURE 2. The signal will be led by passage 38 to output conduit 24. When the pressure in chambers 35 and 36 becomes greater than the pressure in 28 and 30, diaphragms 29 and 31 will bulge in the direction of least pressure, sealing the bottom opening of passage 37, and allowing the signal in cham ber 35 to communicate with passage 38 through passage 37. Thus, the highest of the two input pneumatic signals entering the relay through passages 25 and 32 will be communicated with passage 38 allowing it to exit through conduit 24.

Referring again to FIGURE 1, high select relay 22 transmits an output pneumatic signal of a pressure level equal to the highest of either the signal from biasing relay 44, or the signal from temperature controller 19. This signal is led by conduit 24 to pneumatically operable valve assembly 14. Assembly 14 is comprised of a pneumatic operator 39 which is adjustably attached to both valve 12 and valve 13. Pneumatic operator 39 can be any standard transducer of pneumatic pressure to mechanical motion. Operator 39 is mechanically and adjustably linked to valve 12 by link 40 so that movement of operator 39 opens or closes valve 12. Link 41 is adjustably attached to valves 12 and 13 so that movement of valve 12 moves valve 13 in a predetermined ratio. No further detailed description of valve assembly 14 is given since any pneumatically operated ratio valve assembly may be used.

In operation, the flow of cryogenic fluid in liquid form passing through conduit 1 is sensed by flow controller 16. A proportional output signal is generated by flow controller 16 and a portion of it is routed to high select relay 22. A second portion of the output signal from flow controller 16 is routed to biasing relay 44 and the output from biasing relay 44 is used as the supply for temperature controller 19. The cryogenic fluid is vaporized and superheated in heater 2. Temperature controller 19 senses the temperature of the superheated vapors passing through conduit 5 and generates a proportional signal which is routed to high select relay 22. Flow controller 16 is adjusted to generate an output signal of approximately 9 p.s.i.g. when the flow of cryogenic fluid passing through conduit 1 is normal. Biasing relay 44 is adjusted to generate an output signal of 20 p.s.i.g. when the input signal from flow controller 16 is 9 p.s.i.g. Temperature controller 19 is adjusted with a 20 p.s.i.g. supply signal from biasing relay 44 to generate a 12 p.s.i.g. output signal when the temperature of the vapors in conduit 5 is normal. Valve assembly 14 is adjusted to maintain fuel and air flow rates to combustion chambers 4 in the proper volume of fuel to volume of air ratio so that the desired vapor temperature in conduit 5 is maintained. As the temperature of the superheated vapors in conduit 5 varies, valve assembly 14 will receive a proportional signal up to the maximum range of temperature controller 19 (15 p.s.i.g.), and down to the output signal of flow controller 16 (9 p.s.i.g.). As long as the flow of cryogenic fluid through conduit 1 remains constant this 5 p.s.i.g. range is adequate to maintain a constant temperature of vapors in conduit 5. If the flow of fluid in conduit 1 drops unexpectedly, the output signal from flow controller 16 will drop proportionally. The output signal from biasing relay 44 will also drop proportionally causing the output signal from temperature controller 19 to drop in a corresponding manner. Thus, valve assembly 14 will immediately receive a lower signal when the flow to heater 2 drops, even though the temperature of the vapors in conduit 5 has not yet changed. In the event the flow of fluid in conduit 1 unexpectedly increases the reverse of the steps outlined above will result causing valve assembly 14 to receive an immediate higher signal. Changes in the signal to valve assembly 14 will in turn raise or lower the volume of air and fuel being combusted in combustion chambers 4 which in turn causes more or less heat to be transferred to the fluid being vaporized and superheated. Thus, a system is provided which will cause the heat input to the cryogenic fluid to change immediately upon either flow or temperature changes, and which will maintain a desired temperature thereafter.

Referring now to FIGURES 3 and 4, a heater of the type necessary for carrying out the present invention is illustrated. A plurality of heating tubes 3 are connected in two parallel banks as shown. Return ben'd-s 46 are used to connect the tubes in each bank in series. An inlet connection 47 passes through furnace structure 45 in the lower portion of one vertical wall, and an exit connection 48 passes through furnace structure 45 in the upper portion of the opposite vertical wall. High velocity hot products of combustion are discharged from combustion chambers 4, said chambers having been previously described. Because of the high velocity of the hot products of combustion, eflicient circulation of the hot products of combustion occurs within furnace structure 45 as shown by the arrows in FIGURE 4. Baffles 50 are disposed within furnace structure 45 in the position illustrated to facilitate circulation of the hot products of combustion. After the hot products of combustion have circulated through the heater they exit through openings 49 in the lower portion of opposite walls of furnace structure 2. Since combustion of fuel and air supplied to combustion chambers 4 takes place entirely within chambers 4, and only hot products of combustion enter the furnace structure, heat is transferred to the fluid within heating tubes 3 by a convective heat transfer process only. The rate of convective heat transferred depends on the surface heated, and not on the material of the surface. Thus, layers of ice which may form on the heating tubes 3 due to the very low temperature level of the fluid being heated have little or no effect on the heat transfer rate from the hot products of combustion to the fluid within the heating tubes.

The present invention, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned as well as those inherent therein. While presently preferred embodiments of the invention are given for the purpose of disclosure, numerous changes in the details of construction and arrangement of parts can be made which will readily suggest themselves to those skilled in the art and which are encompassed within the spirit of the invention and the scope of the appended claims.

What is claimed is:

1. A method for vaporizing and superheating cryogenic fluids which comprises:

conducting the fluid to a heater;

detecting the flow rate of said fluid before it enters said heater;

heating said fluid;

detecting the temperature of said fluid after it is heated;

controlling the heating of said fluid in predetermined relation to said detected flow rate and said detected temperature so that said fluid is vaporized and superheated to a constant temperature; and

conducting said fluid to a point of distribution.

2. A method for vaporizing and superheating cryogenic fluids which comprises:

conducting the fluid to a heater;

detecting the flow rate of said fluid before it enters said heater;

passing said fluid through a heater within a plurality of tubes; discharging high velocity hot products of combustion within said heater;

contacting said tubes containing said fluid with said hot products of combustion whereby heat is transferred from said hot products of combustion to said fluid as it passes through said heater;

detecting the temperature of said fluid after it is heated;

controlling the heat transferred to said fluid in predetermined relation to said detected flow rate and said detected temperature so that said fluid is vaporized and superheated to a constant temperature; and conducting said fluid to a point of distribution.

3. A method for vaporizing and superheating cryogenic fluids which comprises:

conducting the fluid to a heater;

detecting the flow rate of said fluid before it enters said heater;

heating said fluid whereby it is vaporized and superheated;

detecting the temperature of said fluid after it is heated;

regulating the heating of said fluid in a predetermined relationship with said detected temperature when said detected flow rate is constant;

regulating the heating of said fluid in predetermined relationship with said detected flow rate when said detected flow rate is not constant; and

conducting said fluid to a point of distribution.

4. A method for vaporizing and superheating cryogenic fluids which comprises:

conducting the fluid to a heater;

detecting the flow rate of said fluid;

passing said fluid through said heater within a plurality of tubes;

mixing combustion air and fuel gas intimately within a gas burner;

burning said mixture of air and gas within said burner thereby creating hot products of combusion within said burner;

releasing said hot products of combustion into said heater;

contacting said tubes containing said fluid with said hot products of combination to said fluid as it passes through said heater thereby vaporizing and superheating said fluid;

detecting the temperature of said fluid after it has passed through said heater;

changing the rate of flow of combustion air and fuel gas to said gas burner in direct proportion to changes in said detected temperature when said detected flow rate is constant;

changing the rate of flow of combustion air and fuel gas to said gas burner in direct proportion to changes in said detected flow rate when said detected flow rate is not constant; and

conducting said fluid to a point of distribution.

5. A system for vaporizing and superheating cryogenic fluids which comprises:

a furnace structure;

a plurality of heating tubes disposed within said furnace structure defining a continuous flow path and having an inlet and an outlet passing through said furnace structure;

means for combusting fuel and air attached to said furnace structure whereby hot products of combustion are discharged into said furnace structure;

a first conduit connected to the inlet of said heating tubes and connected to source of cryogenic fluid pp y;

a second conduit connected to the outlet of said heating tubes and connected to a vapor distribution system;

a third conduit connected to the air inlet of said means for combusting fuel and air;

a first valve connected to said third conduit and connected to a source of air;

a fourth conduit connected to the fuel inlet of said means for combusting fuel and air;

a secnod valve connected to said fourth conduit and connected to a source of fuel;

means for controlling the ratio of the volume of air which passes through said first valve to the volume of fuel which passes through said second valve wherbey said ratio is constant over a range of fuel and air volumes; and

means for detecting fluid flow in said first conduit and for controlling the volume of air and fuel passing through said first and second valves whereby the volume of fuel and air changes in predetermined relationship with said detected fluid flow.

6. A system for vaporizing and superheating cryogenic fluids which comprises:

a furnace structure;

a plurality of heating tubes disposed within said furnace structure defining a continuous flow path and having an inlet and an outlet passing through said furnace structure;

means for combusting fuel and air attached to said furnace structure whereby hot products of combustion are discharged into said furnace structure;

a first conduit connected to. the inlet of said heating tubes and connected to a source of cryogenic fluid supply;

a second conduit connected to the outlet of said heating tubes and connected to a vapor distribution system;

a third conduit connected to the air inlet of said mean for combusting fuel and air;

a first valve connected to said third conduit and connected to a source of air; 1

a fourth conduit connected to the fuel inlet of said means for combusting fuel and air;

a second valve connected to said fourth conduit an connected to a source of fuel;

means for controlling the ratio of the volume of air which passes through said first valve to the volume of fuel which passes through said second valve where by said ratio is constant over a range of fuel and air volumes; and

means for detecting fluid temperature in said second conduit and for controlling the volume of fuel and air passing through said first and second valves whereby the volume of fuel and air changes in predetermined relationship with the detected fluid temperature in said second conduit.

7. A system for vaporizing and superheating cryogeni fluids which comprises:

a furnace structure;

a plurality of heating tubes disposed within said furnace structure defining a continuous flow path and having an inlet and an outlet passing through said furnace structure;

means for combusting fuel and air attached to said furnace structure whereby hot products of combustion are discharged into said furnace structure;

a first conduit connected to the inlet of said heating tubes and connected to a source of cryogenic fluid pp y;

fluid flow responsive means in said first conduit;

a second conduit connected to the outlet of said heating tubes and connected 'to a vapor distribution system;

fluid temperature responsive means in said second conduit;

a third conduit connected to the air inlet of said means for combusting fuel and air;

a first valve connected to said third conduit and connected to a source of air;

a fourth conduit connected to the fuel inlet of said means for combusting fuel and air;

a second valve connected to said fourth conduit and connected to a source of fuel;

means for controlling the ratio of the volume of air which passes through said first valve to the volume of fuel which passes through said second valve whereby said ratio is constant over a range of fuel and air volumes; and

means for controlling the volume of fuel and air passing through said first and second valves regulated by said flow responsive means and said temperature responsive means whereby the volume of fuel and air is changed in predetermined relationship with said flow and temperature.

References Cited UNITED STATES PATENTS KENNETH W. SPRAGUE, Primary Examiner. 

